Method of treating a petroleum fraction with molecular sieve adsorbents



H. V. HESS ETAL METHOD OF' TREATING A PETROLEUM FRACTION WITH Nov. 4, 1958 MOLECULAR SIEVE ADSORBENTS Filed Jan. 25, 1955 nited States 'Patent i METHOD OF TREATING A PETROLEUM FRAC- TION WITH MOLECULAR SIEVE ADSORBENTS Howard V. Hess, Glenham, and Edward R. Christensen, Beacon, N. Y., assignors to The. Texas Company, New York, N. Y., a corporation of Delaware Application January 25, 1955, Serial No. 483,999

7 Claims. (Cl. 20S- 92) This invention relates to a method of treating petroleum fractions. More particularly, this invention relates to a method of treating petroleum fractions containing relatively low molecular weight hydrocarbons such as C4 hydrocarbons and/or C5 hydrocarbons in admixture with relatively high molecularA weight straight chain and non-straight chain hydrocarbons, such as hydrocarbons having a molecular weight in a range Cif-C10 and higher. In accordance with one embodiment of this invention there is provided an improved non-catalytic method for upgrading a petroleum fraction in the naphtha boiling range, such as a naphtha fraction having an initial boiling point (I. B. P.) in a range 35-80 F. and an end point (E. P. in a range about C-425 F., e. g. a light straight run naphtha.

Various processes have been proposed for the treatment of naphtha stocks to produce a high quality, high octane motor fuel. These processes call for the vapor phase treatment of selected petroleum fractions in the gasoline boiling range by contact with an active converting, reforming or isomerizing catalyst, such as a platinum-containing catalyst, (e. g. so-called platforming catalyst), a chromia-alumina catalyst, a cobalt molybdate, a molybdena-alumina catalyst or the like.

During the treatment of these selected petroleum fractions a number of reactions may take place simultaneously, e. g. isomerization, dehydrogenation, cyclization, dehydrocyclization and the like. At the same time some of the higher molecular weight hydrocarbons are converted to lower molecular weight hydrocarbons such as the normally gaseous hydrocarbons, butane, propane and the like with the result that the yield of recoverable normal liquid hydrocarbons is substantially lower than the amount of normally liquid hydrocarbons charged to the catalytic conversion operation.

Accordingly, .it is an object of this invention to provide an improved process for treating a petroleum fraction in the naphtha boiling range.

It is another object of this invention to provide an improved process for upgrading petroleum fractions in lthe naphtha boiling range, said fractions containing straight chain hydrocarbons and non-straight chain hydrocarbons in admiXture with relatively low boiling, low molecular weight hydrocarbons, such as hydrocarbons in a molecular weight range C5 and/or C4 Iand lower.

Another object of this invention is to provide a noncatalytic method for upgrading a hydrocarbon fraction such as a light straight run naphtha fraction whereby a relatively improved, high octane, high quality motor fuel is produced.

Yet another object of this invention is to provide a method of treating a light straight run naphtha containing butane and/or isopentane and/or normal pentane in admixture with higher molecular weight straight chain and non-straight chain hydrocarbons whereby there is produced after treatment, in accordance with this invenrice tion, a naphtha fraction having an improved quality as a motor fuel. l

Another object of this invention is to provide an integrated combination process for treating a naphtha fraction, such as a light straight run naphtha, whereby there is produced a substantially increased amount of high octane normally liquid hydrocarbons as compared with conventional processes operated at the same octane` product level for upgrading such fractions into a high octane motor fuel. i

How these and other objects of this invention are achieved will become more apparent with reference to the accompanying disclosure and drawing which schematically illustrates an embodiment of the practice of this invention.

In accordance with our invention, we have provided an improved operation for treating or converting a petroleum fraction containing straight chain hydrocarbons and non-straight chain hydrocarbons which comprises fractionating said fraction to produce overhead-a selected fraction containing relatively low boiling, low molecular weight hydrocarbons, Vand subjecting the remaining fraction (now containing areduced amount of low molecular weight hydrocarbons) to contact with a solid adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain lhydrocarbons to adsorb straight chain hydrocarbons from said remaining fractionand subsequently blending the aforementioned overhead fraction with the eiuent from the aforesaid adsorption operation, which effluent is substantially free of straight chain hydrocarbons, to produce a blended product having improved qualitiesas motor fuel.

By straight chain hydrocarbon is meant any aliphatic or acyclic or open chain hydrocarbon which does not possess side chain branching or cyclic structure. Representative straight chain hydrocarbons are, of course, the normal parafns and the normal olens, monoor polyolefins, including the straight chain acetylenic hydrocarbons. The non-straight chain hydrocarbons comprise the aromatic and naphthenic hydrocarbons as well -as the isoparaflinic and isoolenic hydrocarbons and the like.

A petroleum fraction suitable for use in the practice of this invention might have an initial boiling point in the range 35l00 F. and an end point in the range of 15G-425 F., more or less. A petroleum fraction suitable for use in the practice of this invention must contain both straight chain and non-straight chain hydro carbons and might have the following composition:

Hydrocarbon type: Percent by volume Unsaturates (including n-olef`1ns and isoolens) 0-50 The straight chain hydrocarbons, e. g. n-parafn -content of a petroleum fraction particularly suitable for use in the practice of this invention is usually in therrange 5-75% by volume;y Typical refinery stocks or fractions, such as a total or wide boiling straight run naphtha, a light straight run naphtha, a thermally cracked: or thermally reformed naphtha may be upgraded to produce an improved motor fuel by employing the practice of this invention. Exemplary of a petroleum fraction suitable for use in the practice of this invention is a light straight run naphtha having a boiling range in the range 45-225 F., andan octane number, clear, in the range 45-85. I

Any solid adsorbent which selectively adsorbs straight straight chain hydrocarbons may be employed in the practice of this invention. It is preferred, however, to employ as the selective adsorbent certain natural or synthetic zeolites or alumino-silicates such as a calcium alumino-silicate e. g. sodium calcium alumino-silicate, which exhibit the property of a molecular sieve, i. e. materials made up of porous crystals or containing pores wherein the pores are of molecular dimension and of uniform size, suhciently large to permit the'entry of straight chain hydrocarbonsto the exclusion of the non-straight chain. hydrocarbons. l

A- particularly suitable selective adsorbent for straight chain hydrocarbons is a calcium alumino-silicate manufactured'byV the Linde Air Products Company and designated Linde-Type 5A Molecular Sieve. The crystals of this particular calcium alumino-silicate, apparently actuallyasodium calcium alumino-silicate, have a pore size or diameter of about 5 angstrom units, sufhciently large to admit straight chain hydrocarbons such as the n-paraiins and the n-olefinslup to at least C1.,z in chain length i to the substantial exclusion of the naphthenic, aromatic hydrocarbons aswell'as isoparans, isobutanes and higher and the-isooletinic hydrocarbons. This particular selective adsorbent is available in various sizes. Any suitable selective adsorbent for straight chain hydrocarbons may' be employed in the practice of this invention. It is contemplated that selective adsorbents having the property of'v selectively adsorbing straight chain hydrocarbons to the substantial exclusion of the non-straight chain hydrocarbons inthe manner of a molecular sieve may be obtained by suitably treating the various oxide gels, especially'metal oxidel gels of the polyvalent amphoteric metal oxides.

Other suitable solid selective adsorbents are known l and include the synthetic and natural zeolites which, when dehydrated, may be described as crystalline zeolites havinga rigid three dimensional anionic network and having interstitial dimension suciently large to adsorb straight chain hydrocarbons but sufficiently small to exclude nonstraight chain-hydrocarbons. The natural zeolite chabazite exhibits such desirable properties. Another suitable natural zeolite is analcite NaAlSi2O6-H-2O which, when dehydrated, and whenl all or part of the sodium is replaced by` calcium, yields a material whicli may be represented by the formula (Ca, Na2)Al2Si4O12.2H2O and which, after suitable conditioning, will adsorb straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons. Other naturally occurring or synthetically prepared zeolites are 'gmelinite, harmotome, phacolite and the like, or suitable modifications of these produced by base exchange are also suitable.

Other solid adsorbents which selectively adsorb straight chain hydrocarbons such as the n-paratlns and the nolens to the substantial exclusion of the non-straight chain hydrocarbons are known.

The adsorption operation or the separation of the straight chain hydrocarbons from an admixture containing the same together with non-straight chain hydrocarbons is effected by direct contact between the mixture containing the straight chain hydrocarbons and the particular selective adsorbent employed. The mixture being separated or treated forthe adsorption of the straight chain hydrocarbons therefrom may be in a liquid phase or in the gaseous or vaporous phase. Any suitable means or. method for eiecting liquid-solid Contact or vaporsolidcontact may be employed in the practice of this in'- vention. For example in presumably the simplest operationaliquid `mixture containing straight chain hydrocarbons to be separated therefrom may be directly contacted with solid selective adsorbent to form a slurry. After.' suilicientttime hasbeen allowed, Vfor the,` adsorption of; the-.straightchain hydrocarbons, the liquid phase is separated from the slurry and the remaining solid adsorbent is separately treated for the removal or desorp-y tion of the straight chain hydrocarbons therefrom.

The solid adsorbent may be in the form of a iixed bed, a moving bed, a fluidized bed, and the mixture undergoing treatment for the separation of the straight chain hydrocarbons therefrom may pass in a direct concurrent or counter-current Contact with the selective adsorbent.` The various known means and methods forV effecting liquid or vapor contact with a solid material are applicable in the practice ofthis invention. n

The adsorption operation may take place at any temperature in the range 50-700" F. and higher depending tain the adsorption temperature in a temperature range ZOO-500 F., more or less.

After the adsorption of the straight chain hydrocarbons by the selective adsorbent employed has beeny carried out tothe desired extent the selective adsorbent is treated to desorb and separately recover the straight chain hydrocarbons therefrom. Desorption ofthe straight chain hydrocarbonsis conveniently effected by the application 'of heat andis preferably effected by contacting the adsorbent with a hot stripping medium such as ilue gas, nitrogen, methane, hydrogen, carbon dioxide, air or oxygen-containing gas under controlled temperature conditions, gas- Y eous Vlow boiling hydrocarbons, such as dry natural gas; superheated steam and the like. Usually a temperature in the range 3DO-1300 F., preferably a temperature in the range 500-1000 F. is sufcient to effect substantially complete desorption of the straight chain hydrocarbons from the selective adsorbent. Although the desorption temperature may be the same as the adsorbent 'temperature, it is sometimes desirable to maintain the desorption temperature about 10U-300 F. higher thanthe adsorp- -tion temperature. As a general rule the desorption temperature should be high enough so thatthe adsorbed straight chain hydrocarbons' are relatively quickly desorbed' without at the same time causing destruction of the selective adsorbent ordecomposition or cracking of the adsorbed-desoroed straight chain hydrocarbons. Liquid water,- such as superheatedwater, i. e. water ata temperature greater than 212 F. at superatmospheric pressure, may also vbe employed as a desorbing medium in the practice of this invention. It is preferred to employ steam or superheated steam as the desorption or stripping medium since, after the desorption of the straight chain hydrocarbons has been effected by superheated steam, the recovery of the straight chain hydrocarbons is effected by simply condensing the steam. It is advantageous to displace the steam now adsorbed to some extent by adsorption within the pores of the adsorbent,.by contacting the adsorbent with a purge gas such as a llue gas, nitrogen, hydrogen, natural gas or the like in order to sweep the steam from the pores of the adsorbent.A

Referring now to the drawing which schematically illustrates an embodiment of the practice of this invention, a suitable feed petroleum fraction such as a naphtha fraction, e. g. a light naphtha fraction, having an end point in the range 15C-425 F. and containing `a substantial amount of hydrocarbons (in the range 20'- by vol.) in the molecular weight range C4-C12is` introduced via line l1 into fractionator l2 wherein it is fractionated to produce overhead a lowboilingor relativelydow'f molecular weight fraction-1 containing-.substantially all of the C4 and C5 hydrocarbons present in the feed fraction. Desirably substantially all of the hydrocarbons present in the overhead fraction should have a boiling point below about 100 F. Preferably, in accordance with one embodiment of this invention fractionator 12 is operated under such conditions with the overhead fraction therefrom containing substantially all of the C4 hydrocarbons and isopentane in the feed, leaving behind a bottoms fraction containing substantially all of the n-pentane and higher molecular weight hydrocarbons originally present in the feed fraction.

The overhead fraction removed from fractionator 12 via line 13 will comprise normal butane and isopentane and varying amounts of n-pentane and even higher molecular weight hydrocarbons depending upon the operation of fractionator 12. Normal butane has an octane number of about 95 and isopentane an octane number of yabout 92; accordingly, these materials are particularly useful as blending components in a motor fuel gasoline. Normal pentane has an octane number of about 61 and accordingly is less desirable as a motor fuel blending agent than the other aforementioned hydrocarbons. n

There is recovered from fractionator 12 a liquid bottoms fraction via line 14 or a vaporous side stream fraction via lines 17 or 17a, Yeach substantially free of C4 and C5 hydrocarbons. The bottoms fraction in line 14 or the side stream fraction in line 17a is introduced into heater wherein it is Vaporized and/or brought up to a suitable adsorption temperature such as a temperature in the range Z50-500 F. Heater 15, if desiredmay be bypassed via line 18. The resulting vaporized bottoms or side stream fraction issues from heater 15 via line 16 and is introduced via line 19 (valve 19a being open and valve 20a being closed) into adsorber 21 wherein it passes downwardly in direct contact with a fixed bed of selective adsorbent which selectively adsorbs thev straight chain hydrocarbons to the substantial eX- clusion of non-straight chain hydrocarbons. Adsorber 21 is operated at a suitable adsorption temperature, as previously indicated, and at a throughput such that the euent issuing from adsorber 21 via line 22 (valve 22a beinglopen) is substantially free of straight chain hydrocarbons. More particularly adsorber 21 is operated under such conditions of temperature and pressure, cons istent'with liquid or vapor phase contacting, and at a throughput (such as a space velocity in the range 0.25- v./hr./v.) such that substantially all of the straight chain hydrocarbons, e. g. straight chain hydrocarbons having a molecular weight in the range CS-Cm and higher, contained in the fraction undergoing treatment, are adsorbed. The eluent issuing from adsorber 21 through line 22 (valve 22a being open) is introduced into line 23 (valve 23a being closed) wherein it is blended or admixed with the previously separated overhead fraction owing in line 13 to produce a blended product having arhigher octane number and improved properties as a motor fuel.

When the selective adsorbent within adsorber 21 has become` substantially `saturated with respect to straight chain hydrocarbons or when theselective adsorbent within' adsorber 21 is no longer able to adsorb straight chain hydrocarbons at the desired rate, valve 19a is closed and Valve 20a is open with the result that the fraction to be treated is introduced via line 20 into adsorber 24 wherein it is contacted with fresh or regenerated selective adsorbent in accordance with this invention as previously described and illustrated in the drawing.

The straight chain hydrocarbons comprising predominantly hydrocarbons in the molecular weight range C6- C12 adsorbents adsorbed by the adsorbent material within adsorber 21 are desorbed therefrom by contacting with a stripping medium introduced via lines 25 and 26 (valve 26a being open and valve 29a being closed) such as ue gas, nitrogen, hydrogen, carbon dioxide, methane andthe like or superheated steam.

The desorption temperature, preferably in the range 300-l300 F., usually in the range 500-1000 F. or 1GO-300 F. higher than the adsorption temperature,

should be such that the adsorbed straight chain hydro-- carbons are relatively quickly desorbed without at the same time causing destruction of the solid selective adsorber or decomposition or cracking of the adsorbent hydrocarbons.

The desorbed straight chain hydrocarbons issuing from adsorber 21 via line 30 (valve 30a being openand valve 32a being closed) together with the gaseous desorbing medium, preferably hydrogen, or after suitable treatment, if desired or necessary for the separation of the straight chain hydrocarbons from the desorbing medium by conventional means such as a cooler or condenser operated in combination with a gas-liquid Iseparator (not illustrated), are introduced via line 32 into converter 31 where they are upgraded, by isomerization, catalytic reforming, thermal reforming or cracking or the like into more valuable motor fuel components, e. g. branched chain hydrocarbons.

The treated or upgraded efluent from converter 31 preferably comprising a mixture of straight chain hydrocarbons and non-straight chain hydrocarbons, including Varying amounts of unsaturated or olefinic hydrocarbons depending upon the operation of converter 31, issues via line 33. A portion or all of this effluent is recycled via line 34 into line 14 for eventual contact with the selective adsorbent, as described hereinabove and illustrated in the drawing, with the result that substantially all of the straight chain hydrocarbons separated from `the fraction undergoing treatment are converted into branched chain hydrocarbons and other more valuable motor fuel components. Moreover, if desired, a portion or all of the effluent issuing from converter 31 via line 33 may be Withdrawn as a separate product as indicated.

After the straight chain hydrocarbons have been desorbed from the adsorbent within adsorber 21 the adsorbent therein is now in condition'to be again contacted with the bottoms and/or side vstream fraction issuing from fractionator 12. Desirably at about this time the adsorbent material within adsorber 24' shall have been substantially saturated with respect to straight chain hydrocarbons. The straight chain hydrocarbons adsorbed by the adsorbent material within adsorber 24 are then desorbed therefrom by introduction of a stripping medium via lines 25 and 29 (valve 29a being open and valve 26a being closed).

lBy operating in the above-indicated.mannerit will be apparent to thoseY skilled in the art that by manipulation of the valves and by adjustment of throughputs and operating conditionsl the described, operations of fractionation, adsorption, desorption, conversion and blending may be carried out continuously.

Exemplary of the practice of this invention a light straight run naphtha having a boiling range 46-226 F. was fractionated to remove overhead substantiallyall of the C4 hydrocarbons contained therein. The resulting bottoms fraction was contacted in the vapor phase with a solid selective adsorbent (Linde Type 5A Molecular Sieve) in order to remove substantially all of the straight run chain hydrocarbons therefrom. The naphtha charge originally had an octane numbenclear of about 72. After fractionation and treatment to remove substantially all the straight chain hydrocarbons therefrom there was recovered a bottoms fraction having an octane number clear `of about 74. However, upon blending back the overhead fractionated C4 hydrocarbons with the treated bottoms fraction, now substantially free of straight chain hydrocarbons, there was produced a blended product having an octane number substantially greater than 74.

Further exemplary of the practice of this invention a light straight run naphtha was distilled at a 122 F. overhead temperature and the resulting residue or bottofrrrs-,fractiom` amounting to 68.3%` by volume of the original `charge to the fractionator wasV treated with Va selective adsorbent for the removal of the straight chain hydrocarbons therefrom. Prior to the removal of the straight` chain hydrocarbons; the fractionator bottoms hadA an ASTM Research Octane Number Clear of 6.9.7. After the removal of the straight chain hydrocarbons the bottoms fraction had an octane number of about 72. However, upon blending back the overhead fraction with the treated bottoms fraction there was produced a blended product having an octane number substantially greater than 72.

FurtherV exemplary of the practice of this invention a light straight run. naphtha having an initial boiling point and anend boilingpoint in the range of 35-375 F.' isV fractionatedl to remove overhead substantially all of the C4., hydrocarbons and the isopentane contained thereinI If desired substantially all of the C hydroA carbons. are rcmovedoverhead with the C4 hydrocarbons. The resulting bottoms fraction is contacted with a selective Vadsnbent toremove substantially all of the straight chain hydrocarbons from the-bottoms fraction soas to produce a treated bottoms fraction substantially freer ofV straight `chain hydrocarbons. This resulting treated bottoms fraction is then Ablended with the aforesaid mentioned overhead fraction comprising C4 hydrocarbons and isopentaneto yieldan upgraded fraction particularly suited as motor fuel component. I

The straightchain hydrocarbons separated from the bottoms fraction and comprising substantially only straight chain hydrocarbons in molecular Weightv range CG-Clz are desorbed from the adsorbentand isomeriz'ed by contact with an isomerizing catalyst, e. g. a platinumcontaining catalyst under straight chain hydrocarbon isomerizing conditions of temperature and pressure, preferably inthe'presen'ce of hydrogen, e. g. stripping hydrogen, to produce .'a'mixture' of straight chain and non-straight chain hydrocarbons. This resulting isornate. has a substantially greater octane number'as compared to? the mixture of straight chain hydrocarbons supplied toY the isom'erizer. a

Exemplary of this particular feature of applicants invention, a mixture ofst'rai'ghtchain hydrocarbons comparable, toa mixture of straight chain hydrocarbons which would4 be recovered as a separate stream in accordance with theA practice of this invention and containing by volume 24% npentane, 56% n-hexane and 20% n-heptane was charged to an isomerizing unit containing a platinumcontaining isomerization catalyst, such as a UOP platforming catalyst. The conditions of isomerization are as follows: operatingA pressure of about 500 p. s. i. g., space. velocity 1.0 v./hr./v., hydrogen recycle rate of 4,000'cubic feet per barrel of charge.

The results obtained are indicated in Table No. I.

The isomate product having an octane number 58.0 was then treated at a temperature of 235 F. and at substantially atmospheric pressure and at a space velocity of 1.0 v./hr./v. with a solid selective adsorbent to remove substantially all of thek straight chain hydrocarbons therefrom.

The resulting. inished product had an octane number of 77.1 clear and 94.0 w./3.0 cc. TEL/gallon (ASTM micro-research) at-a Yyield of approximately 60 volume percent. This upgraded nished product is advantageously adsorbed With the previously separatedV and blended overhead-treated fractions as indicated in tl'e drawing. i'

Vln view of the foregoing, it is apparent that we have n provided a non-catalytic method of upgrading a petroleum fractionrv in a naphtha boiling range whereby an improved higherV octane motor fuel is obtained. The practice this invention is particularly applicable to upgrading of light naphtha, especially light straight run naphtliawhich is usually not suitable for upgrading by the various' catalyticY reforming processes. The process of this invention is particularly applicable to the upgrading of light straight run naphtlias containing acyclic, satura `A hydrocarbons (normalV parans, isoparains') in ii" amount in thel range of 2090% by volume. 'r lThis patent application is a continuation-impart` ofk our co-pending application Serial No. 478,426,` filed?l December 29, 1954, which is particularly directed to ai petroleum treating process involving the separation" ofz straight chain hydrocarbons from a petroleum fractio followed by conversion of the resulting treated'strai'ght p chain hydrocarbon free fraction.4 This parent applica#Y tion also discloses fractionating a petroleum fraction to? remove an overhead fraction andblending ther remveldi` overhead fraction with the remaining treatediconvertedA petroleumfraction. This' application is also relatedv to' or co-p'ending patent application Serial No. 483;9 8,r led Ianuary 25, 1955, which discloses a petrole'urn treating operation involving converting a petroleumfrac'-y ti'on, such as .by catalytic reforming, followed by adsorption treatment to produce a' treated fractionbsrbl stantially free of straight chain hydrocarbons. application also discloses fractionating a converted or." catalytic reformed petroleum fraction to remove` o ieir-V head a fraction comprising C4 hydrocarbons, treatingthe remaining catalytic reformed fraction" to separa the straightv chain hydrocarbons therefrom andlbleriding the overhead fraction into the resultingtreatedcatalyticI reformed product. 1 v

As will be apparent to thoseA skilled in the artn'any' modifications, substitutions andv changesv are-p"'ossil5l`e without departing from'the spirit'or scope ofthis irfv tion.

We claim: i w p y l. AY method of treating a petroleum fraction" havi'g' an end pointin the range l0O-425u `F. and;` containing ai substantiafamount of C4 and C5 hydrok'zarbo'ns wh h`v comprises fractionating said'petroleumfractionto rem overhead substantially' all of the C4 and C5 hydrocarb subjecting the remaining petroleum fraction tocn with a molecular sieve alumino-silicate selective adsor ent which selectively adsorbs straight chain hydr carbons to the substantial exclusion of non-straigl'it-cha hydrocarbons to adsorb straightchainhydrocarbonsfro said remaining petroleum fraction, recovering'fr'oin fthe" aforesaid yadsorption operation a treated fraction'substaii' tially free of straight chain hydrocarbons andebleiidfng with said recovered treatedfraction the C4 and`C5-hydroV carbons separatedov'erhead'in the aforesaid fractionation l operation.' Y K p 2'. A methodvin accordance with claim 1 vv'ber'ei` straight chain hydrocarbons are desorbed fromzsaidiad-`l sorbentand isomerized to produce a mixture of straight. chain 4 and non-straight' chain hydrocarbons;`

3; A method of treatingja petroleum'ifraction naphtha boiling range and containing a substantial "amount of acyclic hydrocarbons'in the molecular Weight'raxigeCg` and lower which comprises subjecting' said petroleum fraction to fractionation tofremove overhead substantially allV thehydrocarb'ons therein having a' boilingpoint not greater than about 10Gcv F., subjectingi'the remaining petroleurnrfraction to' contact with a' molecularsi'eve alumino-silicatesolid selective adsorbent which selectively adsorbs istraight chain hy'fdrocarborisV to the-substantialfex clusion of non-straight'chain hydrocarbonst adsorb straight chain hydrocarbons therefrom thereby yielding a treated fraction substantially free of straight chain hydrocarbons and blending the overhead from the aforementioned fractionation operation with said treated straight chain hydrocarbon free fraction recovered from the adsorption operation.

4. A method of treating a light straight run naphtha having an end point in the range 1D0-225 F. said naphtha containing a major amount of saturated hydrocarbons, including a substantial amount of C4 and C5 hydrocarbons, which comprises fractionating said naphtha to remove overhead substantially all of the C4 and C5 hydrocarbons in said naphtha, subjecting the remaining naphtha fraction to contact with a molecular sieve alumino-silicate selective adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb straight chain hydrocarbons from said remaining naphtha fraction, recovering from the aforesaid adsorption operation a treated naphtha fraction substantially free of straight chain hydrocarbons and blending with said recovered treated fraction said C4 and C5 hydrocarbons separated overhead in the aforesaid fractionation operation.

5. A method in accordance with claim 4 wherein the straight chain hydrocarbons are desorbed from said adsorbent and isomerized to produce an isomate mixture of straight and non-straight chain hydrocarbons, contacting said isomate with a selective adsorbent to adsorb substantially all of the straight chain hydrocarbons therefrom to produce a treated isomate substantially free of straight chain hydrocarbons and blending said treated isomate with said treated fraction and said C5 and C5 hydrocarbons.

6. A method of treating a light straight run naphtha having an end point in the range 1D0-225 F., said naphtha containing a major amount of saturated hydrocarbons, aliphatic and alicyclic hydrocarbons, including a substantial amount of C4 and C5 hydrocarbons, which comprises fractionating said naphtha to remove overhead substantially all of the C4 and C5 hydrocarbons in said naphtha, subjecting the remaining naphtha fraction to contact with a molecular sieve alumino-silicate selective adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb straight chain hydrocarbons from said remaining naphtha fraction, recovering from the aforesaid adsorption operation a treated naphtha fraction substantially free of straight chain hydrocarbons, desorbing the straight chain hydrocarbons from said adsorbent and reforming said straight chain hydrocarbons to produce a reformate mixture of straight chain and non-straight chain hydrocarbons, contacting said reformate with a molecular sieve alumino-silicate selective adsorbent to adsorb substantially all of the straight chain hydrocarbons therefrom to produce a treated reformate and blending together said treated reformate, said treated naphtha fraction and said C4 and C5 hydrocarbons.

7. A method of treating a petroleum fraction having an end point in the range -425 F. and containing a substantial amount of C4 and C5 hydrocarbons which comprises fractionating said petroleum fraction to remove overhead substantially all of the C4 and C5 hydrocarbons, subjecting the remaining petroleum fraction to contact with a molecular sieve alumino silicate selective adsorbent which selectively adsorbs straight vchain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb straight chain hydrocarbons from said remaining petroleum fraction, recovering from theA aforesaid adsorption operation a treated fraction substantially free of straight chain hydrocarbons, blending the recovered treated fraction with the C.; and C5 hydrocarbons separated overhead in the aforesaid fractionation operation, desorbing the adsorbed straight chain hydrocarbons from said adsorbent by contacting said adsorbent with gaseous hydrogen and isomerizing the resulting desorbed straight chain hydrocarbons in the presence of the hydrogen employed to desorb the adsorbed straight chain hydrocarbons from the selective adsorbent with a platinum-containing isomerization catalyst under isomerizing conditions.

References Cited in the file of this patent UNlTED STATES PATENTS 2,146,039 Whiteley Feb. 7, 1939 2,304,187 Marschner Dec. 8, 1942 2,425,535 Hibshman Aug. 12, 1947 2,442,191 Black May 25, 1948 2,522,426 Black Sept. 12, 1950 2,602,772 Haensel July 8, 1952 

1. A METHOD OF TREATING A PETROLEUM FRACTION HAVING AN END POINT IN THE RANGE 100-425*F. AND CONTAINING A SUBSTANTIAL AMOUNT OF C4 AND C5 HYDROCARBONS WHICH COMPRISES FRACTIONATING SAID PETROLEUM FRACTION TO REMOVE OVERHEAD SUBSTANTIALLY ALL OF THE C4 AND C5 HYDROCARBONS, SUBJECTING THE REMAINING PETROLEUM FRACTION TO CONTACT WITH A MOLECULAR SIEVE ALUMINO-SILICATE SELECTIVE ADSORBENT WHICH SELECTIVELY ADSORBS STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIAL EXCLUSION OF NON-STRAIGHT CHAIN HYDROCARBONS TO ADBORB STRAIGHT CHAIN HYDROCARBONS FROM SAID REMAINING PETROLEUM FRACTION, RECOVERING FROM THE AFORESAID ADSORPTION OPERATION A TREATED FRACTION SUBSTANTIALLY FREE OF STRAIGHT CHAIN HYDROCARBONS AND BLENDING WITH SAID RECOVERED TREATED FRACTION THE C4 AND C5 HYDROCARBONS SEPARATED OVERHEAD IN THE AFORESAID FRACTIONATION OPERATION. 